1. Field of the Invention
The present invention relates to a waveguide used in microwave and millimeter wave bands and, more particularly, to a technique for enabling a wavelength on the waveguide to be changed to thereby being able to reduce devices such as a phase shifter and a phased array antenna in size compared with conventional devices.
2. Description of the Related Art
Waveguides similar to the present invention are explained in United States Publication No. 2011/0181373 and WO 2010/050122.
United States Publication No. 2011/0181373 is common to WO 2010/050122 and the present invention in a basic structure for confining high-frequency energy to realize a waveguide. WO 2010/050122 is an invention that realizes a phase shifter commonly known as a trombone type using the waveguide of United States Publication No. 2011/0181373 and further realizes a phased array antenna using a plurality of trombone-type phase shifters.
A conventional waveguide and a conventional phase shifter are explained below with reference to figures.
FIG. 12 shows the structure of the conventional waveguide. Reference numeral 1200 denotes the conventional waveguide, 1201 denotes a first conductor plate, 1202 denotes a second conductor plate, 1203 denotes a ridge-shaped conductor, and 1204 denotes columnar conductors. As shown in FIG. 12, the first conductor plate 1201 and the second conductor plate 1202 are disposed with the surfaces thereof opposed to each other. Further, on the first conductor plate 1201, the ridge-shaped conductor 1203 is provided and a plurality of columnar conductors 1204 are cyclically provided in regions on both sides of the ridge-shaped conductor. The height of the columnar conductors 1204 is selected to be ¼ wavelength and the distance between the distal ends of the columnar conductors 1204 and the second conductor plate 1202 is selected as to be ⅛ wavelength to make it possible to efficiently confine high-frequency energy. The sectional shape of the columnar conductors 1204 is set to a square of ⅛ wavelength on each side. The disposition cycle of the columnar conductors 1204 is set to ¼ wavelength.
A principle of transmission of the high-frequency energy by the conventional waveguide 1200 configured as explained above is explained. A parallel flat waveguide is formed by the first conductor plate 1201 and the second conductor plate 1202 disposed with the surfaces thereof opposed to each other. However, since the columnar conductors 1204 having the height of ¼ wavelength are disposed on the surface of the first conductor plate 1201 in a two-dimensional direction at a cycle of ¼ wavelength sufficiently short compared with a wavelength, a surface formed by connecting the distal ends of the columnar conductors 1204 acts as a magnetic wall and an electric current cannot flow. Therefore, the transmission of the high-frequency energy by a parallel flat mode, which is a propagation mode of the parallel flat waveguide, is suppressed. On the other hand, since only the surface of the ridge-shaped conductor 1203 is in a state in which conductors, which are electric walls, are connected, an electric current flows, whereby a waveguide in which the high-frequency energy is transmitted is realized along the ridge-shaped conductor 1203.
The conventional phase shifter is explained with reference to FIG. 13. FIG. 13 shows the sectional shape of a phase shifter in which a pair of the conventional waveguides shown in FIG. 12 is used. In FIG. 13, reference numeral 1300 denotes the conventional phase shifter, 1301 and 1302 denote the conventional waveguides, 1303 and 1304 denote first conductor plates, 1305 and 1306 denote second conductor plates, 1307 denotes an input port, 1308 denotes an output port, 1309 denotes a through-hole, 1310 denotes a transmission line of high-frequency energy, 1311 denotes an intermediate layer, and 1312 denotes a slide direction of the intermediate layer. As shown in FIG. 13, the two conventional waveguides 1301 and 1302 are stuck together such that the positions of ridge-shaped conductors thereof overlap each other and with the backs of the first conductor plates thereof opposed to each other. That is, FIG. 13 shows the sectional shape in the center of the ridge-shaped conductors.
Further, as shown in FIG. 13, in the conventional phase shifter 1300, the input port 1307 is provided in the second conductor plate 1305 of one conventional waveguide 1301, the output port 1308 is provided in the second conductor plate 1306 of the other conventional waveguide 1302, and the through-hole 1309 is provided in the same position of the first conductor plates 1303 and 1304 of the two conventional waveguides 1301 and 1302. Choke structures by distal end short-circuit holes 1313 and 1314 having depth of ¼ of a waveguide wavelength are cut in positions apart from each other by ¼ of the waveguide wavelength in the input port 1307 and the output port 1308, ridge-shaped conductors 1315 and 1316 are cut in positions apart from each other by ¼ of the waveguide wavelength in the through-hole 1309, and choke structures by columnar conductors 1317 and 1318 having height of ¼ wavelength are provided on the outer sides of the ridge-shaped conductors 1315 and 1316, whereby the transmission line 1310 of high-frequency energy is formed. In the conventional phase shifter 1300 configured as explained above, the length of the transmission line 1310 of high-frequency energy formed in a trombone shape is changed by moving the intermediate layer 1311 in the slide direction 1312. Consequently, the phase shifter 1300 changes a phase of the high-frequency energy that enters from the input port 1307 and exits to the output port 1308.